The present invention relates generally to medical devices and particularly to expandable heart valve prostheses especially for use in minimally-invasive surgeries.
Prosthetic heart valves are used to replace damaged or diseased heart valves. In vertebrate animals, the heart is a hollow muscular organ having four pumping chambers: the left and right atria and the left and right ventricles, each provided with its own one-way valve. The natural heart valves are identified as the aortic, mitral (or bicuspid), tricuspid and pulmonary valves. Prosthetic heart valves can be used to replace any of these naturally occurring valves, although repair or replacement of the aortic or mitral valves is most common because they reside in the left side of the heart where pressures are the greatest.
Where replacement of a heart valve is indicated, the dysfunctional valve is typically cut out and replaced with either a mechanical valve, or a tissue valve. Tissue valves are often preferred over mechanical valves because they typically do not require long-term treatment with anticoagulants. The most common tissue valves are constructed with whole porcine (pig) valves, or with separate leaflets cut from bovine (cow) pericardium. Although so-called stentless valves, comprising a section of porcine aorta along with the valve, are available, the most widely used valves include some form of stent or synthetic leaflet support. Typically, a wireform having alternating arcuate cusps and upstanding commissures supports the leaflets within the valve, in combination with an annular stent and a sewing ring. The alternating cusps and commissures mimic the natural contour of leaflet attachment. Importantly, the wireform provides continuous support for each leaflet along the cusp region so as to better simulate the natural support structure.
A conventional heart valve replacement surgery involves accessing the heart in the patient""s thoracic cavity through a longitudinal incision in the chest. For example, a median sternotomy requires cutting through the sternum and forcing the two opposing halves of the rib cage to be spread apart, allowing access to the thoracic cavity and heart within. The patient is then placed on cardiopulmonary bypass which involves stopping the heart to permit access to the internal chambers. Such open heart surgery is particularly invasive and involves a lengthy and difficult recovery period.
Recently, a great amount of research has been done to reduce the trauma and risk associated with conventional open heart valve replacement surgery. In particular, the field of minimally invasive surgery (MIS) has exploded since the early to mid-1990s, with devices now being available to enable valve replacements without opening the chest cavity. MIS heart valve replacement surgery still requires bypass, but the excision of the native valve and implantation of the prosthetic valve are accomplished via elongated tubes or cannulas, with the help of endoscopes and other such visualization techniques.
Some examples of MIS heart valves are shown in U.S. Pat. No. 5,980,570 to Simpson, U.S. Pat. No. 5,984,959 to Robertson, et al., and PCT Publication No. WO 99/334142 to Vesely. Although these and other such devices provide various ways for collapsing, delivering, and then expanding a xe2x80x9cheart valvexe2x80x9d per se, none of them disclose an optimum structure for tissue valves. For instance, the publication to Vesely shows a tissue leaflet structure of the prior art in FIG. 1, and an expandable inner frame of the invention having stent posts in FIGS. 3A-3C. The leaflets are xe2x80x9cmounted to the stent posts 22 in a manner similar to that shown in FIG. 1.xe2x80x9d Such a general disclosure stops short of explaining how to construct an optimum valve. In particular, the means of attaching the leaflets to the MIS stent is critical to ensure the integrity and durability of the valve once implanted. All of the prior art MIS valves fall short in this regard.
In view of the foregoing, it is evident that an improved minimally-invasive heart valve that addresses the apparent deficiencies in existing expandable heart valves is necessary and desired.
The present invention provides an expandable prosthetic heart valve for placement in a host heart valve annulus, comprising an expandable stent system adapted to be delivered in a collapsed state to an implantation site and expanded, and a plurality of prosthetic leaflets attached to the stent system. Each leaflet has an approximately semi-circular cusp edge terminating at each end in commissure portions, and a coapting edge extending between the commissure portions. Each leaflet is attached to the stent system substantially entirely along the cusp edge and at both commissure portions, with a coapting edge remaining unattached. The stent system may comprise an expandable generally annular tissue-engaging base and an elastic generally annular wireform attached thereto. The base is adapted to be delivered in a radially collapsed state and expanded into contact with the host annulus. The annular wireform defines a plurality of upstanding commissures and a plurality of arcuate cusps between adjacent commissures, and the prosthetic leaflets are attached to the wireform along the cusps and commissures, wherein the wireform and leaflets are configured to be radially compressed.
In one embodiment, the heart valve includes a plurality of upstanding posts attached to one of the tissue-engaging base and elastic wireform, each post having a connector. A plurality of mating connectors are provided on the other of the tissue-engaging base and elastic wireform for mating with the post connectors. The posts and mating connectors may be provided for each commissure and each cusp of the elastic wireform so that the valve includes a number of posts and mating connectors equal to the number of commissures plus the number of cusps. Further, the expandable stent system may include an undulating wireform defining a plurality of commissures and a plurality of cusps between adjacent commissures. The cusp edge of each of the prosthetic leaflets attaches along a wireform cusp, and the commissure portions of each leaflet terminate in outwardly extending tabs that each attach to a wireform commissure, wherein tabs from adjacent leaflets are attached together at each of the wireform commissures.
In another aspect of the invention, an expandable prosthetic heart valve for placement in a host heart valve annulus is provided. The heart valve comprises an expandable stent portion and an elastic leaflet portion connectable to the stent portion. The stent portion defines an inflow end of the valve and is adapted to be delivered in a collapsed state and expanded into contact with the host annulus. The leaflet portion forms a one-way flow occluder on an outflow end of the valve and includes an elastic wireform defining alternating cusps and commissures and prosthetic tissue attached substantially entirely therealong. The stent portion desirably includes a tubular member and a plurality of connectors, and wherein a plurality of connectors are provided on the elastic wireform for mating with the tubular member connectors. The wireform connectors may be provided on each commissure and on each cusp of the wireform so that the valve includes a number of mating connectors equal to the number of commissures plus the number of cusps. In a preferred embodiment, the prosthetic tissue comprises a plurality of individual leaflets secured along the alternating cusps and commissures of the elastic wireform. Additionally, the wireform may have a fabric covering, wherein the individual leaflets are stitched along the fabric covering. The fabric covering continues toward an inflow end of the valve in a skirt that surrounds the stent portion and is adapted to be captured between the expanded stent portion and the host annulus. A plurality of posts rigidly may connect to the stent portion and extend upward within the skirt into mating connection with the elastic wireform.
In a still further aspect, the present invention provides a two-part expandable prosthetic heart valve for placement in a host heart valve annulus, comprising:
a leaflet subassembly having a wireform defining a plurality of upstanding commissures and a plurality of arcuate cusps extending between adjacent commissures, a midpoint of each cusp being located approximately equidistant from the adjacent commissures;
a generally annular tissue-engaging base defining an axis; and
a system for connecting the leaflet subassembly and the tissue-engaging base, including a plurality of mating connectors on the leaflet subassembly and on the tissue-engaging base, wherein one connector each is provided at each commissure, and one at each cusp midpoint.
In the two-part heart valve, the tissue-engaging base preferably comprises an expandable tubular member that is deliverable to the host annulus in a collapsed state and expandable into contact with the host annulus to secure the valve therein. Furthermore, the tissue-engaging base forms an inflow end of the valve, and the system for connecting the leaflet subassembly and tissue-engaging base includes a plurality of posts coupled to the tubular member and having varying lengths extending away from the inflow end of the valve. A first plurality of posts each having a first length connects with the wireform commissures, and a second plurality of posts each having a second length connects with the wireform cusps shorter than the first length. The mating connectors may be configured to be joined together by axial compression, preferably with a snap-fit configuration.
A further aspect of the invention includes a prosthetic heart valve having a support stent and a flexible tubular member. The support stent includes a tubular base along an inflow end a plurality of generally axially-extending commissure posts disposed evenly around the tubular base on an outflow end thereof. The flexible tubular member has a prosthetic section attached to the commissure posts so as to define a plurality of the prosthetic valve leaflets between the posts, and a fabric section connected to the base. The prosthetic section and fabric section are desirably both generally tubular and attached together at a seam, wherein the seam is spaced from the outflow end of the tubular base so that only the fabric section of the flexible tubular member contacts the tubular base. The commissure posts each may have an axial slot, wherein the tubular member is primarily located within the posts except for a plurality of loops that extend outward through each slot on each post. A plurality of inserts sized larger than the slots may be provided, each of which insert is captured within a loop extending outward through each slot to retain the loop through the slot. In a preferred embodiment, the commissure posts are integrally formed with the base, the base and commissure posts being initially formed from a flat section of material, wherein the commissure posts initially extend from the inflow end of the base and are bent 180xc2x0 to extend alongside the base and project beyond the base at the outflow end thereof.
A prosthetic heart valve of the present invention has a support stent including a tubular base along an inflow end. A plurality of generally axially-extending commissure posts each having an axial slot is disposed evenly around the tubular base on an outflow end thereof. A flexible tubular member having an outflow edge is primarily located within the posts except for a plurality of loops that extend outward through each slot on each post. Further, a plurality of inserts sized larger than the slots are provided, each of which insert is captured within a loop extending outward through each slot to retain the loop through the slot, the outflow edge of the tubular member defining a plurality of valve leaflets. The tubular base may be plastically-expandable from a first size adapted for minimally invasive delivery, to a second, functional size that fits within a heart valve annulus.
A method of minimally-invasive heart valve replacement surgery on a patient is also provided by the present invention. The method includes the steps of:
providing an annular tissue-engaging base, the base being expandable from a collapsed state;
providing a generally annular elastic wireform subassembly having a plurality of prosthetic leaflets connected thereto, the elastic wireform subassembly having a relaxed, expanded size and a compressed, reduced size;
connecting the wireform and leaflets to the base to form a heart valve;
delivering the heart valve with the connected base in its collapsed state and wireform subassembly in its reduced size to an annulus of the patient""s heart valve being replaced; and
expanding the base into its expanded state in contact with the annulus.
The step of delivering the heart valve to the annulus may be accomplished by passing the valve through the patient""s vasculature or via a minimally-invasive port in the patient""s chest. The tissue-engaging base may plastically-expandable from its collapsed state to its expanded state, and the step of expanding the plastically-expandable base comprises inflating a balloon within the annular base.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.